P5091

We showed that knockdown of USP7 or treatment with USP7 inhibitor P5091 suppressed liver cancer growth by promoting CD8+ T cell activity in Hepa1-6 xenograft mice and in HepG2 or Huh7 cells co-cultured with T cells, whereas USP7 overexpression produced the opposite effect...In an immunocompetent liver cancer mouse model, the dual blockade of USP7 and LAG3 resulted in a superior antitumor activity compared with anti-LAG3 therapy alone. We conclude that USP7 diminishes CD8+ T cell activity by a USP7/PRDM1 positive feedback loop on FGL1 production in liver cancer; USP7 might be a promising target for liver cancer immunotherapy.

However, the chemoresistance of cancer cells to USP7i (P22077 and P5091) and mechanisms to overcome it have not yet been investigated. Inhibition of HSF1 and PERK significantly sensitized cancer cells to USP7i-induced cytotoxicity. Our study demonstrated that the ER stress-PERK axis is responsible for chemoresistance to USP7i, and inhibiting PERK is a potential strategy for improving the anticancer efficacy of USP7i.

Treatment of the CLL cell line MEC1 and primary CLL patient samples with DUB inhibitors including PR-619 (pan-DUBi), P5091 (USP7i) and HBX19818 (USP7i) alone reduces the phosphorylation of AKTS437 and FOXO1T24, indicating that DUBs play a role in inhibiting FOXO1 activity. Additionally, FOXO1 activity studies demonstrated significant activation of FOXO1 upon ibrutinib treatment, which was further enhanced in the USP7 KD and combination with USP7i. These studies suggest that selective DUBs play a role in BCR-mediated signalling to aid in the promotion of CLL cell survival and chemo-resistance through FOXO1 inhibition, and targeting these DUBs enhance FOXO1 activity leading to cell cycle arrest and apoptosis.

Pharmacological inhibition of USP7 by P5091 phenocopies the shUSP7-induced senescent phenotype. We show that the bifunctional histone deacetylase (HDAC)/LSD1 inhibitor domatinostat has an additive antitumor effect, eliminating P5091-induced senescent cells, paving the way to a therapeutic combination for individuals with melanoma.

Moreover, combined treatment with the USP7-specific inhibitor P5091 and EZH2 inhibitors, such as GSK126, EPZ6438, and DZNep, induced synergistic inhibitory effects on cell migration, invasion, and sphere-forming potential in prostate cancer cells. Collectively, our findings revealed that the promotion of the malignancy-associated characteristics of prostate cancer cells by USP7 was in part due to EZH2 stabilization. Thus, we suggest that simultaneous treatment with a USP7 inhibitor and an EZH2 inhibitor could be a rational strategy for treating EZH2-dependent cancers.

Genetic knockdown or pharmacological inhibition (P5091 or P22027) of USP7 reduced the proliferation rate of lung cancer cells and decreased the capacity of colony formation of lung cancer cells in vitro, whereas lung cancer cells growth inhibition by FTO knockdown is restored by overexertion of USP7. Collectively, our findings demonstrate that the m6A demethylase FTO promotes the growth of NSCLC cells by increasing the expression of USP7.